The present invention relates generally to voltage recorders and in particular the present invention relates to transient voltage recorders. Voltage transients caused by atmospheric disturbances are often present in power and communication lines. These transients are especially noticeable following a nearby lightning strike. Although most electronic equipment has some form of transient protection, some limitations exist on maximum sustainable transient levels. This limitation is determined by both the amplitude and duration that the equipment can withstand before permanent damage occurs. Electronic components and equipment can have an immediate, easy to detect failure when they are subjected to voltages larger than their maximum rated values. Obvious failures include short-circuited components, open components, or non-functional components. Transient voltages can also alter characteristics of an electronic component without obvious sign of failure. Unless there is a way to determine that transient voltages were present, such anomalies can remain undetected and eventually lead to premature failure of a component.
Transient voltage recorders have been used for many years to monitor voltages and currents on cables. Common sources of transient voltages include large electronic motors, switching of power equipment, induced voltages from nearby lightning strikes, and direct lightning strikes. Transients generated by sources other that lightning tend to have frequency components well below one megahertz, which most commercial transient recorders can detect. On the other hand, recent research has shown that lightning induced transients contain voltage peaks that rise in a small fraction of a microsecond and contain frequencies exceeding tens of megahertz. Commercially available recorders cannot measure these fast peaks. Thus, incorrect indications of the magnitude of the peak value of transients are provided.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for a transient voltage recorder that can accurately characterize lightning induced voltage transients.
The above-mentioned problems with voltage transient recorders and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
In one embodiment, a transient voltage recorder comprises an input to receive a voltage signal, an amplifier coupled to the input, an amplifier gain adjust circuit coupled to adjust a gain of the amplifier, and a sample and hold circuit coupled to the amplifier.
In another embodiment, a transient voltage recorder comprises an input to receive a voltage signal, an amplifier coupled to the input, an amplifier gain adjust circuit coupled to adjust a gain of the amplifier and an analog-to-digital converter coupled to the amplifier. The transient voltage recorder includes a voltage threshold circuit, and a controller coupled to the analog-to-digital converter, the voltage threshold circuit and the amplifier gain adjust circuit. The controller monitors an output of the amplifier in response to the voltage threshold circuit and determines if the output from the amplifier is clipped or is too low. The controller further controls the amplifier gain adjust circuit to adjust the gain of the amplifier.
In yet another embodiment, a transient voltage recorder comprises a plurality of input amplifiers each coupled to receive one of a plurality of input voltage signals, and an amplifier gain adjust circuit coupled to adjust a gain of the plurality of amplifiers. An analog-to-digital converter is coupled to outputs of the plurality of amplifiers. Further, a voltage threshold circuit is coupled to the outputs of the plurality of amplifiers. The voltage transient recorder further comprises a non-volatile memory device, a time circuit, and a controller coupled to the analog-to-digital converter, the voltage threshold circuit, the non-volatile memory device and the amplifier gain adjust circuit. The controller monitors the outputs of the plurality of amplifiers in response to the voltage threshold circuit and determines if the outputs of the plurality of amplifiers are magnitude clipped or have a low signal. The controller further controls the amplifier gain adjust circuit to adjust the gain of the amplifier.
A method of recording a transient voltage is provided that comprises monitoring an input voltage signal, detecting when the input voltage signal exceeds a pre-determined threshold voltage level, determining if an input amplifier gain it too large or too small for the input voltage signal, and reducing or increasing the gain of the input amplifier to capture the input voltage signal.